METHOD AND APPARATUS FOR MEASURING IMPURITY CONCENTRATION IN NITRIDE SEMICONDUCTOR LAYER

Abstract

To provide a non-contact and non-destructive technique for measuring impurity concentration in nitride semiconductor layers.SOLUTION: A measuring device 1 for measuring the impurity concentration of a nitride semiconductor layer 100 comprises an intensity ratio calculation unit 44 for calculating an intensity ratio of the intensity of the impurity bound exciton emission to the intensity of the free exciton emission (intensity of the impurity bound exciton emission / intensity of the free exciton emission) from the free exciton emission and impurity bound exciton emission contained in the photoluminescence of the nitride semiconductor layer and a concentration identification unit 46 for identifying an impurity concentration in the nitride semiconductor layer based on the intensity ratio.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The technology disclosed in this specification relates to a measurement method and a measurement device for measuring the impurity concentration of a nitride semiconductor layer. [Background technology]

[0002] Non-Patent Document 1 discloses a technique for measuring the impurity concentration of a nitride semiconductor layer by utilizing the Hall effect. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Masahiro Horita et al., “Hall-effect measurements of metalorganic vaporphase epitaxy-grown p-type homoepitaxial GaN layers with various Mg concentrations”, Japanese Journal of Applied Physics. 56, 031001(2017) Summary of the Invention [Problem to be solved by the invention]

[0004] In order to utilize the technology of Non-Patent Document 1, an electrode that makes ohmic contact with the nitride semiconductor layer must be formed. For example, it is known that it is difficult to form an electrode with good ohmic characteristics for a nitride semiconductor layer such as p-type gallium nitride (GaN). This specification aims to provide a technology for measuring the impurity concentration of a nitride semiconductor layer in a non-contact and non-destructive manner. [Means for solving the problem]

[0005] This specification discloses a method for measuring an impurity concentration in a nitride semiconductor layer (100). This method can include an intensity ratio calculation step of calculating an intensity ratio of the intensity of the impurity bound exciton emission to the intensity of the free exciton emission from free exciton emission and impurity bound exciton emission contained in the photoluminescence of the nitride semiconductor layer (intensity of impurity bound exciton emission / intensity of free exciton emission), and a concentration specifying step of specifying the impurity concentration in the nitride semiconductor layer based on the intensity ratio.

[0006] The intensity ratio of the intensity of the impurity bound exciton luminescence / the intensity of the free exciton luminescence has a relationship that depends on the impurity concentration of the nitride semiconductor layer. The above measurement method calculates the intensity ratio of the intensity of the impurity bound exciton luminescence / the intensity of the free exciton luminescence from the photoluminescence of the nitride semiconductor layer, and can specify the impurity concentration of the nitride semiconductor layer based on the intensity ratio. In this way, the above measurement method can measure the impurity concentration of the nitride semiconductor layer in a non-contact and non-destructive manner.

[0007] This specification discloses a measuring device (1) for measuring an impurity concentration in a nitride semiconductor layer (100). This measuring device may include an intensity ratio calculation unit (44) for calculating an intensity ratio (intensity of impurity bound exciton emission / intensity of free exciton emission) of an intensity of the impurity bound exciton emission to an intensity of the free exciton emission from free exciton emission and impurity bound exciton emission contained in photoluminescence of the nitride semiconductor layer, and a concentration specifying unit (46) for specifying an impurity concentration in the nitride semiconductor layer based on the intensity ratio.

[0008] The intensity ratio of the intensity of the impurity bound exciton luminescence / the intensity of the free exciton luminescence has a relationship that depends on the impurity concentration of the nitride semiconductor layer. The measuring device calculates the intensity ratio of the intensity of the impurity bound exciton luminescence / the intensity of the free exciton luminescence from the photoluminescence of the nitride semiconductor layer, and can specify the impurity concentration of the nitride semiconductor layer based on the intensity ratio. In this way, the measuring device can measure the impurity concentration of the nitride semiconductor layer in a non-contact and non-destructive manner. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram illustrating a schematic configuration of a measurement device for measuring an impurity concentration in a nitride semiconductor layer. [Diagram 2] (A) Photoluminescence spectra of a nitride semiconductor layer measured at an absolute temperature of 5 K, together with the photoluminescence spectra at five different acceptor concentrations. (B) Photoluminescence spectra of a nitride semiconductor layer measured at an absolute temperature of 40 K, together with the photoluminescence spectra at five different acceptor concentrations. [Diagram 3] FIG. 1 shows a calibration curve prepared by plotting the relationship between the intensity ratio (ABE / FE) and the acceptor concentration for each of five standard samples. [Figure 4] 1 is a flowchart illustrating an example of an acceptor concentration measurement processing method executed by a measurement apparatus. [Diagram 5] 13 is a flowchart illustrating a modified example of an acceptor concentration measurement processing method executed by the measurement apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, a measuring method and a measuring device for measuring the impurity concentration of a nitride semiconductor layer will be described with reference to the drawings. The measurement of the impurity concentration described below is one process for manufacturing a nitride semiconductor device, and is performed before or during the manufacturing of the nitride semiconductor device. Here, the nitride semiconductor layer broadly means a semiconductor layer made of a III-V group semiconductor containing nitrogen as a group V element. As an example, the nitride semiconductor layer may be made of gallium nitride (GaN), aluminum gallium nitride (AlGaN), or indium gallium nitride (InGaN). The impurity referred to in this specification is an impurity that becomes an acceptor or a donor, and is an impurity that determines the conductivity type of the nitride semiconductor layer. In addition, the impurity concentration referred to in this specification is an acceptor concentration or a donor concentration, and the term "impurity concentration" is used to mean both. The technology disclosed in this specification is applicable to measuring the acceptor concentration due to atoms such as Mg, Be, Zn, C, and Ca, and is applicable to measuring the donor concentration due to atoms such as Si, Ge, O, and Sn. In the following, an example will be described in which the nitride semiconductor layer is made of gallium nitride (GaN), and the acceptor concentration due to magnesium (Mg) contained in the nitride semiconductor layer is measured.

[0011] 1 shows a schematic configuration of a measurement apparatus 1 for measuring the impurity concentration of a nitride semiconductor layer 100. The measurement apparatus 1 includes an irradiation unit 10, a spectroscope 20, a photodetector 30, and a processing unit 40.

[0012] The irradiation unit 10 is configured to irradiate the nitride semiconductor layer 100 with excitation light, and includes at least a laser light source and a focusing lens. The excitation light emitted from the laser light source is irradiated onto the nitride semiconductor layer 100 via the focusing lens. The excitation light emitted from the laser light source only needs to have energy larger than the band gap of the nitride semiconductor layer 100.

[0013] The spectrometer 20 is configured to separate the photoluminescence emitted from the nitride semiconductor layer 100 into a predetermined wavelength range. As described later, the measurement device 1 uses free exciton luminescence and acceptor bound exciton luminescence contained in the photoluminescence in order to measure the acceptor concentration due to magnesium in the nitride semiconductor layer 100. For this reason, the spectrometer 20 is only required to be configured to be able to separate at least the free exciton luminescence and the acceptor bound exciton luminescence. Note that the respective light energies of the free exciton luminescence and the impurity bound exciton luminescence (meaning to include both the acceptor excitation light and the donor excitation light) depend on the type of nitride semiconductor and the type of impurity of the measurement target sample. Therefore, the spectrometer 20 is only required to be configured to separate the predetermined free exciton luminescence and the impurity bound exciton luminescence based on the type of nitride semiconductor and the type of impurity of the measurement target sample.

[0014] The photodetector 30 is configured to convert the light dispersed by the spectrometer 20 into an electrical signal having a magnitude corresponding to the intensity of the light, and output the electrical signal to the processing unit 40. The photodetector 30 may be configured as a photomultiplier tube, a CCD detector, or the like, as one example.

[0015] The processing unit 40 has a PL measuring unit 42, an intensity ratio calculating unit 44, and a concentration specifying unit 46. The PL measuring unit 42, the intensity ratio calculating unit 44, and the concentration specifying unit 46 are physically configured with a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. The processing unit 40 is configured to execute an acceptor concentration measurement process using the functions of the PL measuring unit 42, the intensity ratio calculating unit 44, and the concentration specifying unit 46 by, for example, loading a program stored in the ROM into the RAM and executing the program loaded into the RAM by the CPU.

[0016] The PL measurement unit 42 is configured to receive the electrical signal output from the photodetector 30 and calculate the light intensity from the magnitude of the electrical signal. In this way, the PL measurement unit 42 can acquire the spectrum of the photoluminescence emitted from the nitride semiconductor layer 100.

[0017] The intensity ratio calculation unit 44 is configured to measure the intensity of free exciton luminescence and the intensity of acceptor bound exciton luminescence contained in the photoluminescence spectrum acquired by the PL measurement unit 42. Here, FIG. 2 shows the photoluminescence spectrum of the nitride semiconductor layer 100. (A) shows the photoluminescence spectrum when the measurement temperature is an absolute temperature of 5 K, and (B) shows the photoluminescence spectrum when the measurement temperature is an absolute temperature of 40 K. Note that in each of (A) and (B), the acceptor concentration due to magnesium is 1.2×10 17 cm -3 , 2.1×10 17 cm -3 , 3.0×10 17 cm -3 , 5.7×10 17 cm -3 , 1.2×10 18 cm -3 The photoluminescence spectrum at each of the above conditions is also shown. "ABE (Acceptor Bound Exciton)" indicates the intensity of light emitted due to acceptor bound excitons, "DBE (Donor Bound Exciton)" indicates the intensity of light emitted due to donor bound excitons, and "FE (Free Exciton)" indicates the intensity of light emitted due to free excitons. The acceptor bound excitons include a type called neutral acceptor bound excitons, and the donor bound excitons include a type called neutral donor bound excitons. The intensity ratio calculation unit 44 measures the intensity that is the peak value of the acceptor bound excitons (ABE) and the intensity that is the peak value of the free exciton emission (FE).

[0018] As shown in Figure 2, the intensity of free exciton luminescence (FE) tends to decrease as the acceptor concentration increases. Furthermore, it can be seen that the intensity of free exciton luminescence (FE) also strongly depends on the measurement temperature. For example, when the measurement temperature is 5K absolute, and the acceptor concentration is 1.2×10 18 cm -3 The intensity of the free exciton luminescence (FE) at the nitride semiconductor layer 100 is hardly observable. Therefore, in order to observe the intensity of the free exciton luminescence (FE), it is desirable to adjust the measurement temperature according to the acceptor concentration of the nitride semiconductor layer 100.

[0019] The intensity ratio calculation unit 44 is configured to determine whether the intensities of the free exciton luminescence (FE) and the acceptor bound exciton luminescence (ABE) are observable. In this example, the intensity of the free exciton luminescence (FE) is smaller than the intensity of the acceptor bound exciton luminescence (ABE). Therefore, the intensity ratio calculation unit 44 can determine whether the intensity of the acceptor bound exciton luminescence (ABE) is observable by determining whether the intensity of at least the free exciton luminescence (FE) is observable. When the intensity of the free exciton luminescence (FE) is observable, the intensity ratio calculation unit 44 calculates the intensity ratio (ABE / FE) of the intensity of the acceptor bound exciton luminescence (ABE) to the intensity of the free exciton luminescence (FE) and outputs it to the concentration specification unit 46. Here, whether the intensity of the free exciton luminescence (FE) is observable may be determined by whether the intensity of the free exciton luminescence (FE) exceeds a predetermined threshold, as an example.

[0020] When the intensity of the free exciton luminescence (FE) is not observable, the intensity ratio calculation unit 44 does not calculate the intensity ratio (ABE / FE). In this case, the measurement device 1 operates to increase the measurement temperature and acquire a new photoluminescence spectrum of the nitride semiconductor layer 100. The measurement device 1 repeats increasing the measurement temperature and acquiring a photoluminescence spectrum until the intensity of the free exciton luminescence (FE) is observable. In this manner, the measurement device 1 determines the measurement temperature at which the intensity of the free exciton luminescence (FE) is observable. The intensity ratio calculation unit 44 calculates the intensity ratio (ABE / FE) at the determined measurement temperature and outputs it to the concentration determination unit 46.

[0021] The intensity ratio (ABE / FE) is the acceptor concentration due to magnesium (N A ) is dependent on the acceptor concentration. FIG. 3 shows the relationship between the intensity ratio (ABE / FE) and the acceptor concentration for five standard samples 51, 52, 53, 54, and 55, each of which has a different acceptor concentration. The acceptor concentrations of the five standard samples 51, 52, 53, 54, and 55 are values ​​confirmed by Hall effect measurement, CV measurement, or SIMS measurement. As shown in FIG. 3, the relationship between the intensity ratio (ABE / FE) and the acceptor concentration (N A ) have a specific relationship depending on the concentration region. The measuring device 1 creates a calibration curve using a plurality of standard samples 51, 52, 53, 54, and 55 having different acceptor concentrations. The calibration curve may be created by determining a function with the acceptor concentration as the response variable and the intensity ratio (ABE / FE) as the dependent variable.

[0022] The concentration specifying unit 46 is configured to specify the acceptor concentration of the nitride semiconductor layer 100 based on the intensity ratio (ABE / FE) of the nitride semiconductor layer 100 calculated by the intensity ratio calculating unit 44. Specifically, the concentration specifying unit 46 can specify the acceptor concentration from the intersection point where the calculated intensity ratio (ABE / FE) of the nitride semiconductor layer 100 intersects with the calibration curve.

[0023] FIG. 4 shows an example of a flowchart of the acceptor concentration measurement process executed by the measurement device 1. First, the measurement device 1 executes steps S1 to S4 for creating a calibration curve. The measurement device 1 measures the photoluminescence of each of a plurality of standard samples having different acceptor concentrations (step S1). Specifically, the measurement device 1 emits excitation light from the irradiation unit 10 and irradiates the standard samples with the excitation light. The measurement device 1 further measures the photoluminescence emitted from the standard samples with the PL measurement unit 42 and obtains a photoluminescence spectrum.

[0024] Next, the measuring device 1 causes the intensity ratio calculation unit 44 to measure the intensity of the acceptor bound exciton luminescence and the intensity of the free exciton luminescence in each of the multiple standard samples (step S2). Next, the measuring device 1 causes the intensity ratio calculation unit 44 to calculate the intensity ratio (ABE / FE) of the acceptor bound exciton luminescence to the intensity of the free exciton luminescence in each of the multiple standard samples (step S3). The measuring device 1 creates a calibration curve from the relationship between the data of the intensity ratio (ABE / FE) obtained from each of the multiple standard samples and the acceptor concentration (step S4).

[0025] Next, the measuring device 1 measures the photoluminescence of the nitride semiconductor layer 100, which is the measurement target sample (step S5). The method of measuring the photoluminescence is the same as that of the standard sample. Next, the measuring device 1 causes the intensity ratio calculation unit 44 to measure the intensity of the acceptor bound exciton luminescence and the intensity of the free exciton luminescence of the nitride semiconductor layer 100 (step S6). Next, the measuring device 1 causes the intensity ratio calculation unit 44 to calculate the intensity ratio (ABE / FE) of the intensity of the acceptor bound exciton luminescence to the intensity of the free exciton luminescence of the nitride semiconductor layer 100 (step S7). Next, the measuring device 1 causes the concentration determination unit 46 to determine the acceptor concentration of the nitride semiconductor layer 100 from the intersection point where the intensity ratio (ABE / FE) of the nitride semiconductor layer 100 intersects with the calibration curve (step S8).

[0026] In this way, the measurement apparatus 1 can measure the acceptor concentration of the nitride semiconductor layer 100 based on the intensity ratio (ABE / FE) calculated from the photoluminescence of the nitride semiconductor layer 100. The photoluminescence of the nitride semiconductor layer 100 can be acquired in a non-contact and non-destructive manner. Therefore, the measurement apparatus 1 can measure the acceptor concentration of the nitride semiconductor layer 100 in a non-contact and non-destructive manner.

[0027] 5 shows an example of a modified flowchart of the acceptor concentration measurement process executed by the measurement apparatus 1. First, the measurement apparatus 1 sets a measurement temperature (step S11). Next, the measurement apparatus 1 measures the photoluminescence of the nitride semiconductor layer 100, which is a sample to be measured (step S12).

[0028] Next, the measuring device 1 causes the intensity ratio calculation unit 44 to determine whether the intensity of the free exciton luminescence of the nitride semiconductor layer 100 is an observable intensity. For example, when the intensity of the free exciton luminescence is equal to or lower than a predetermined threshold, the measuring device 1 returns to step S11 and resets the measuring temperature. In this case, the measuring device 1 resets the measuring temperature to a temperature that is increased by a predetermined temperature width from the measuring temperature determined to be unobservable. When the intensity of the free exciton luminescence exceeds a predetermined threshold, the measuring device 1 proceeds to step S14 and advances the acceptor concentration measurement process. As described above, if the free exciton luminescence is observable, it can be determined that the acceptor excitation light is also observable. In this way, the measuring device 1 can determine the measuring temperature at which the intensities of the free exciton luminescence and the acceptor bound exciton luminescence of the nitride semiconductor layer 100 are observable, and at the same time, can acquire the intensity of the acceptor bound exciton luminescence and the intensity of the free exciton luminescence at that measuring temperature (step S14).

[0029] Next, the measurement apparatus 1 causes the intensity ratio calculation unit 44 to calculate the intensity ratio (ABE / FE) of the intensity of the acceptor bound exciton luminescence to the intensity of the free exciton luminescence of the nitride semiconductor layer 100 (step S15).

[0030] Next, the measuring device 1 executes steps S16 to S19 for creating a calibration curve. The measuring device 1 measures photoluminescence for each of a plurality of standard samples having different acceptor concentrations at the determined measurement temperature (step S16). Next, the measuring device 1 causes the intensity ratio calculation unit 44 to measure the intensity of acceptor bound exciton luminescence and the intensity of free exciton luminescence for each of the plurality of standard samples (step S17). Next, the measuring device 1 causes the intensity ratio calculation unit 44 to calculate the intensity ratio (ABE / FE) of the intensity of acceptor bound exciton luminescence to the intensity of free exciton luminescence for each of the plurality of standard samples (step S18). The measuring device 1 creates a calibration curve from the relationship between the data of the intensity ratio (ABE / FE) obtained from each of the plurality of standard samples and the acceptor concentration (step S19). Note that instead of this example, calibration curves for each temperature measured at various temperatures may be created in advance.

[0031] Next, the measurement apparatus 1 causes the concentration specifying unit 46 to specify the acceptor concentration of the nitride semiconductor layer 100 from the point where the calculated intensity ratio (ABE / FE) of the nitride semiconductor layer 100 intersects with the calibration curve (step S20).

[0032] The intensity of free exciton luminescence of the nitride semiconductor layer 100 is highly temperature dependent. According to the above measurement method, the acceptor concentration of the nitride semiconductor layer 100 can be measured after adjusting the measurement temperature. Therefore, the acceptor concentration of the nitride semiconductor layer 100 can be measured satisfactorily.

[0033] The features of the technology disclosed in this specification are summarized below. Note that the technical elements described below are independent technical elements that exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing.

[0034] This specification can disclose a measuring method for measuring an impurity concentration of a nitride semiconductor layer. This measuring method can include an intensity ratio calculation step of calculating an intensity ratio of the intensity of the impurity bound exciton emission to the intensity of the free exciton emission from the free exciton emission and the impurity bound exciton emission contained in the photoluminescence of the nitride semiconductor layer (intensity of impurity bound exciton emission / intensity of free exciton emission), and a concentration specifying step of specifying the impurity concentration of the nitride semiconductor layer based on the intensity ratio. When measuring an acceptor concentration among the impurity concentrations of the nitride semiconductor layer, an intensity ratio of the intensity of the acceptor bound exciton emission to the intensity of the free exciton emission is used. When measuring a donor concentration among the impurity concentrations of the nitride semiconductor layer, an intensity ratio of the intensity of the donor bound exciton emission to the intensity of the free exciton emission is used.

[0035] The above measuring method may further include a calibration curve creating step of calculating the intensity ratio for each of a plurality of standard samples having different impurity concentrations and creating a calibration curve showing a relationship between the intensity ratio and the impurity concentration. In this case, the concentration specifying step may include measuring the impurity concentration of the nitride semiconductor layer based on the calibration curve.

[0036] In the intensity ratio calculation step of the above measurement method, a measurement temperature at which the free exciton luminescence and the impurity bound exciton luminescence contained in the photoluminescence of the nitride semiconductor layer can be observed may be determined by changing a temperature of the nitride semiconductor layer, and the intensity ratio may be calculated at the determined measurement temperature. In this case, in the calibration curve creation step of the above measurement method, the intensity ratio of each of the plurality of standard samples may be calculated at the determined measurement temperature.

[0037] In the above measuring method, the impurity concentration of the nitride semiconductor layer may be an acceptor concentration due to magnesium.

[0038] The present specification may disclose a measuring device for measuring an impurity concentration in a nitride semiconductor layer. The measuring device may include an intensity ratio calculating unit for calculating an intensity ratio of the impurity bound exciton emission to the intensity of the free exciton emission from free exciton emission and impurity bound exciton emission contained in the photoluminescence of the nitride semiconductor layer (intensity of impurity bound exciton emission / intensity of free exciton emission), and a concentration specifying unit for specifying the impurity concentration in the nitride semiconductor layer based on the intensity ratio.

[0039] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Furthermore, the technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives is itself technically useful. [Explanation of symbols]

[0040] 1: measuring device, 10: irradiating unit, 20: spectroscope, 30: photodetector, 40: processing unit, 42: PL measuring unit, 44: intensity ratio calculating unit, 46: concentration specifying unit, 100: nitride semiconductor layer

Claims

1. A method for measuring an impurity concentration in a nitride semiconductor layer (100), comprising the steps of: an intensity ratio calculation step of calculating an intensity ratio of the intensity of the impurity bound exciton emission to the intensity of the free exciton emission from the free exciton emission and the impurity bound exciton emission contained in the photoluminescence of the nitride semiconductor layer (intensity of the impurity bound exciton emission / intensity of the free exciton emission); and a concentration specifying step of specifying an impurity concentration of the nitride semiconductor layer based on the intensity ratio, The impurity concentration of the nitride semiconductor layer is an acceptor concentration due to magnesium.

2. The method further includes a calibration curve creation step of calculating the intensity ratio for each of a plurality of standard samples having different impurity concentrations, and creating a calibration curve showing a relationship between the intensity ratio and the impurity concentration, The measurement method according to claim 1 , wherein in the concentration specifying step, the impurity concentration of the nitride semiconductor layer is specified based on the calibration curve.

3. In the intensity ratio calculation step, a measurement temperature at which the free exciton luminescence and the impurity bound exciton luminescence contained in the photoluminescence of the nitride semiconductor layer can be observed is determined by changing a temperature of the nitride semiconductor layer, and the intensity ratio is calculated at the determined measurement temperature; The measurement method according to claim 2 , wherein in the calibration curve creation step, the intensity ratio of each of the plurality of standard samples is calculated at the determined measurement temperature.

4. A measuring device (1) for measuring an impurity concentration in a nitride semiconductor layer (100), comprising: an intensity ratio calculation unit (44) that calculates an intensity ratio (intensity of impurity bound exciton emission / intensity of free exciton emission) of an intensity of the impurity bound exciton emission to an intensity of the free exciton emission from free exciton emission and impurity bound exciton emission contained in the photoluminescence of the nitride semiconductor layer; a concentration specifying unit (46) that specifies an impurity concentration of the nitride semiconductor layer based on the intensity ratio, The impurity concentration of the nitride semiconductor layer is an acceptor concentration due to magnesium.

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